Napier carried out a series of experiments, measuring errors in compass navigation, and published his findings in 1851.

In the early 1970s, he designed the first automatic digital device to measure refractive errors in the eye.

It measures errors and sends correction signals to two satellites that relay them to planes in flight.

Technical means for measuring offer limited resolution and respective digitizing errors.

A focometer is an instrument that measures refractive errors and is intended to provide rural or economically disadvantaged populations spherical eyeglass prescriptions without the need for complicated protocols, expensive equipment, or electricity.

Focometers measure spherical refractive errors.

And while all this is going on, he and his colleagues will argue over definitions, measuring errors and interpretations until they mostly agree.

An optometer is an instrument for measuring refractive errors in eyes-in order that corrective lenses may be prescribed.

By measuring errors in the machines themselves, rather than simply measuring errors in the final products, problems can be dealt with and fixed earlier in the manufacturing process.